Simulation of the Solid Electrolyte Interphase Layer in Lithium Metal Batteries – a Systematic Study

Instability of the anode-electrolyte interface and uncontrolled lithium (Li) dendrite growth pose serious safety concerns hindering the commercialization of high energy density Li metal batteries (LMBs). In particular, the Solid Electrolyte Interphase (SEI) layer is a key factor causing instability at the interface. The SEI layer is formed due to side reactions between Li, electrons, and electrolyte. When stable, this layer acts as a passivation layer that allows for transport of Li ions (Li+) to the anode while keeping the electrolyte and anode separated reducing the side reactions along the anode surface. However, following the initial growth of the SEI layer, the diffusion and reaction kinetics initiate dendrite growth, leading to the rupture of the SEI layer and exposure of fresh metallic Li. The high reactivity of Li metal results in continuous and rapid growth due to high reaction rates and fast kinetics. Finally, the SEI layer will reform over the exposed Li leading to excess electrolyte consumption causing permanent capacity loss and reduced coulombic efficiency. We present a systematic computational study of the various methods that are used to simulate the impact of the SEI layer, with varying level of complexity. Methods that were studied include varying reaction rates based on thinning and fracture of the SEI layer, a fixed SEI layer that possesses effective transport properties based on the porosity and tortuosity of the compact layer, the consideration of surface energy, and a competing current system that accounts for the ions consumed due to the parasitic SEI formation reaction.